The present invention relates to a technology for supporting creation and validation of a digital sign for a digital document to be canonicalized before adding and validating the digital sign.
In order to prevent disguises and falsifications, a digital sign may be often attached to a digital document described in Extensible Markup Language (XML) (called XML document, hereinafter) in a transmitting information processor having created the XML document (called document creating device, hereinafter). The digital sign is created by encrypting, with a private key of the document creating device, a message digest value (hash value) of an XML document to be signed.
On the other hand, an information processor having received the XML document with the digital sign (called sign validating device, hereinafter) calculates a message digest value of the XML document to be signed, decrypts the digital sign with a public key of the document creating device and compares the results of both of them so that the validity of the XML document can be confirmed.
Incidentally, the sign validating device fails in validating an XML document since even a change in numbers of blanks and line breaks while the XML document with the digital sign is being transmitted changes the digest value of the XML document. Therefore, when a sign is added to an XML document and the sign of the XML document is validated, both of the document creating device and sign validating device perform processing for canonicalizing the XML document before the calculation of a digest value thereof. The canonicalizing processing is being standardized by World Wide Web Consortium (W3C). For example, Boyer, John, “Canonical XML Version 1.0, W3C Recommendation 15 Mar. 2001”, [online], 15 Mar. 2001, [searched on 20 Jul. 2004], Canonical XML on Web page, URL:http://www.w3.org/TR/xml-c14n (hereinafter, referred to as Document 1) and Boyer, John and et al 2, “Exclusive XML Canonicalization Version 1.0, W3C Recommendation 18 Jul. 2002.”, [online], 18 Jul. 2002, [searched on 20 Jul. 2004], Exclusive XML Canonicalization on Web page, URL:http://www.w3.org/TR/xml-exc-c14n/ (hereinafter, referred to as Document 2) are publicly available as standard specifications.